I completely agree with you that the adult thing to do would be all three having a conversation together, in which they agree what a reasonable amount of ‘gift’ is, and also hopefully Jennie agrees that Phoebe needs to do work to earn more during the long vac. But how good a storyline would that make?
I’m afraid it strikes me as slightly cheap to suggest everyone at Oxford is well off and flashing the cash, but also realistic to think phoebe needs to learn about managing her money.
And of course, she also has a mother and stepmother who seem to be completely forgotten about. Hayley would surely be sensible about this if she still existed!